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general description the max6680/max6681 are precise, two-channel digi- tal thermometers. each accurately measures the tem- perature of its own die and one remote pn junction and reports the temperature on a 2-wire serial interface. the remote junction can be a diode-connected transistor like the low-cost npn type 2n3904 or pnp type 2n3906. the remote junction can also be a common- collector pnp, such as a substrate pnp of a micro- processor. the max6680/max6681 include pin-programmable default temperature thresholds for the overt output, which provides fail-safe clock throttling or system shut- down. in addition, the devices are pin programmable to select whether the overt output responds to either the local, remote, or both temperatures. the 2-wire serial interface accepts standard system management bus (smbus) commands such as write byte, read byte, send byte, and receive byte to read the temperature data and program the alarm thresholds and conversion rate. the max6680/max6681 can func- tion autonomously with a programmable conversion rate, which allows the control of supply current and temperature update rate to match system needs. for conversion rates of 4hz or less, the remote sensor tem- perature can be represented in extended mode as 10 bits + sign with a resolution of 0.125?. when the con- version rate is 8hz, output data is 7 bits + sign with a resolution of 1?. the max6680/max6681 also include an smbus timeout feature to enhance system reliability. the max6681 is an upgrade to the max6654. the max6680/max6681 remote accuracy is ?? with no calibration needed. they are available in a 16-pin qsop package and operate throughout the -55? to +125? temperature range. applications features ? two alarm outputs: alert and overt ? pin-programmable threshold for overt limit ? programmable under/overtemperature alert limit ? dual channel: measures remote and local temperature ? 11-bit, 0.125? resolution for remote temperature measurements ? high accuracy ?? (max) from +60? to +100? (remote) ? no calibration required ? smbus/i 2 c-compatible interface ? smbus timeout prevents smbus lockup max6680/max6681 ?? fail-safe remote/local temperature sensors with smbus interface ________________________________________________________________ maxim integrated products 1 clock data to system shutdown stby crit1 crit0 gnd overt smbclk reset smbdata v cc interrupt to p 0.1 f 2200pf dxn microprocessor dxp 200 ? 10k ? each alert 3.3v int_sel sens_sel add1 add0 max6680 max6681 typical operating circuit ordering information 19-2305; rev 1; 1/05 for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. part temp range pin-package max6680 mee -55 c to +125 c 16 qsop max6681 mee -55 c to +125 c 16 qsop smbus is a trademark of intel corp. i 2 c is a trademark of philips corp. pin configurations appear at end of data sheet. desktop computers notebook computers servers thin clients workstations
max6680/max6681 ?? fail-safe remote/local temperature sensors with smbus interface 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (circuit of typical operating circuit, v cc = 3.0v to 5.5v, t a = -25? to +125?, unless otherwise specified. typical values are at v cc = 3.3v and t a = +25?.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. v cc ...........................................................................-0.3v to +6v dxp.............................................................-0.3v to (v cc + 0.3v) dxn ......................................................................-0.3v to +0.8v smbclk, smbdata, alert , overt .....................-0.3v to +6v reset, int_sel, stby , add0, add1.....................-0.3v to +6v crit1, crit0, sens_sel ........................................-0.3v to +6v smbdata, alert , overt , current ..................-1ma to +50ma dxn current ......................................................................?ma continuous power dissipation (t a = +70?) 16-pin qsop (derate 8.3mw/? above +70?) ..........664mw junction temperature .....................................................+150? storage temperature range ............................-65? to +150? lead temperature (soldering, 10s) ................................+300? parameter symbol conditions min typ max units 1c temperature resolution, legacy mode 8 bits 0.125 ? temperature resolution, extended mode 11 bits t rj = +60? to +100?, v cc = 3.3v -1.0 +1.0 t rj = +50? to +120?, v cc = 3.3v -2.0 +2.0 rem ote tem p er atur e e r r or ( n ote 1) t rj = -55? to +125?, v cc = 3.3v -3.0 +3.0 ? t a = +60? to +100?, v cc = 3.3v -1.5 +1.5 t a = 0? to +125?, v cc = 3.3v -3.0 +3.0 local temperature error t a = -55? to +125?, v cc = 3.3v (note 2) -5.0 +5.0 ? line regulation 3.0v v cc 5.5v 0.2 0.6 m c/v supply voltage range v cc 3.0 5.5 v undervoltage lockout threshold uvlo falling edge of v cc disables adc 2.60 2.80 2.95 v undervoltage lockout hysteresis 90 mv power-on reset (por) threshold v cc , falling edge 1.5 2.0 2.5 v por threshold hysteresis 90 mv legacy 62.5 conversion time extended 125 ms standby supply current smbus static 3 10 a operating current during conversion 0.55 1.0 ma 0.25 conversions/s 35 70 average operating current (note 3) 2 conversions/s 120 180 ? dxp and dxn leakage current in standby mode 2 a high level 80 100 120 remote-diode source current i rj low level 8 10 12 ?
max6680/max6681 ?? fail-safe remote/local temperature sensors with smbus interface _______________________________________________________________________________________ 3 electrical characteristics (continued) (circuit of typical operating circuit, v cc = 3.0v to 5.5v, t a = -25? to +125?, unless otherwise specified. typical values are at v cc = 3.3v and t a = +25?.) note 1: t a = +25? to +85?. note 2: if both the local and the remote junction are below t a = -20?, then v cc > 3.15v. note 3: conversions done in extended mode. for legacy mode, current is approximately half. note 4: timing specifications guaranteed by design. note 5: the serial interface resets when smbclk or smbdata is low for more than t timeout . note 6: a transition must internally provide at least a hold time to bridge the undefined region (300ns max) of smbclk? falling edge. parameter symbol conditions min typ max units crit0, crit1, add0, add1, reset, int_sel, sens_sel logic input low voltage v il 0.8 v logic input high voltage v ih 2.4 v input leakage current i leak -1 +1 ? ( alert , overt ) output low sink current v ol = 0.4v 1 ma output high leakage current v oh = 5.5v 1 a smbus interface (smbclk, smbdata, stby ) logic input low voltage v il 0.8 v v cc = 3.0v 2.2 logic input high voltage v ih v cc = 5.5v 2.4 v input leakage current i leak v in = gnd or v cc ? ? output low sink current i ol v ol = 0.6v 6 ma input capacitance c in 5pf smbus-compatible timing (note 5) serial clock frequency (note 5) f scl 100 khz bus free time between stop and start condition t buf 4.7 ? start condition setup time 4.7 ? repeat start condition setup time t su:sta 90% to 90% 50 ns start condition hold time t hd:sta 10% of smbdata to 90% of smbclk 4 s stop condition setup time t su:sto 90% of smdclk to 90% of smbdata 4 s clock low period t low 10% to 10% 4.7 ? clock high period t high 90% to 90% 4 s data setup time (note 6) t hd:dat 250 ns receive scl/sda rise time t r 1s receive scl/sda fall time t f 300 ns pulse width of spike suppressed t sp 050ns smbus timeout (note 5) smbdata low period for interface reset 25 37 45 ms
max6680/max6681 ?? fail-safe remote/local temperature sensors with smbus interface 4 _______________________________________________________________________________________ typical operating characteristics (t a = +25?, unless otherwise noted.) max6680/81 toc01 supply voltage (v) standby supply current ( a) 5.0 4.5 4.0 3.5 1 2 3 4 5 6 7 8 9 10 0 3.0 5.5 standby supply current vs. supply voltage max6680/81 toc02 conversion rate (hz) operating supply current ( a) 8.0000 4.0000 2.0000 1.0000 0.5000 0.2500 0.1250 100 200 300 400 500 600 0 0.0625 average operating supply current vs. conversion rate 8hz is 1 c resolution max6680/81 toc03 temperature ( c) temperature error ( c) 125 100 75 50 25 0 -25 -2 -1 0 1 2 3 -3 -50 150 temperature error vs. remote-diode temperature max6680/81 toc04 temperature ( c) temperature error ( c) 100 50 0 -2 -1 0 1 2 3 -3 -50 150 local temperature error vs. die temperature max6680/81 toc05 frequency (hz) temperature error ( c) 1m 10k 100 0 0.2 0.4 0.6 0.8 1.0 1.2 -0.2 110m 100k 1k 10 100m temperature error vs. power-supply noise frequency v in = 100mv square wave applied to v cc with no 0.1 f v cc capacitor local diode remote diode max6680/81 toc06 frequency (hz) temperature error ( c) 10m 1m 100k 10k 1k 100 10 -1 0 1 2 3 4 5 -2 1 100m temperature error vs. common-mode noise frequency v in = 100mv p-p square wave ac-coupled to dxn max6680/81 toc07 frequency (hz) temperature error ( c) 10m 1m 100k 10k 1k 0 1 2 3 -1 100 100m temperature error vs. differential noise frequency v in = 10mv p-p square wave applied to dxp-dxn max6680/81 toc08 dxp-dxn capacitance (nf) temperature error ( c) 90 80 70 60 50 40 30 20 10 -4 -3 -2 -1 0 1 -5 0100 temperature error vs. dxp-dxn capacitance
max6680/max6681 ?? fail-safe remote/local temperature sensors with smbus interface _______________________________________________________________________________________ 5 pin description pin max6680 max6681 name function 12v cc supply voltage input, 3v to 5.5v. bypass v cc to gnd with a 0.1? capacitor. a 200 ? series resistor is recommended, but not required for additional noise filtering. see the typical operating circuit . 2, 5 1, 5 crit1, crit0 hardware-programmable default alarm threshold for overt limits. use table 4 to set default temperatures. 3 3 dxp combined remote-diode current source and a/d positive input for remote- diode channel. do not leave dxp floating; connect dxp to dxn if no remote diode is used. place a 2200pf capacitor between dxp and dxn for noise filtering. 44dxn combined remote-diode current sink and a/d negative input. dxn is internally biased to one diode drop above ground. 6 6 add1 smbus address select pin (table 9). add0 and add1 are sampled upon power-up. excess capacitance (>50pf) at the address pins when floating may cause address-recognition problems. 7 7 reset reset input. drive reset high to set all registers to their default values (por state). drive reset low or leave floating for normal operation. 8 8 gnd ground 99 overt overtemperature active-low output. open drain. 10 10 add0 smbus slave address select pin (see add1). 11 11 alert smbus alert (interrupt) active-low output. open drain. 12 12 smbdata smbus serial-data input/output, open drain 13 13 int_sel input. connect high or leave floating to conform to the standard smbus alert protocol. see the alert interrupts section . connect to gnd to invoke comparator mode, where alert is asserted whenever any of the temperature conditions is violated by the remote sensor. in this mode, alert can only be deasserted by the condition returning within the temperature limits by enabling the mask bit in the configuration register. 14 14 smbclk smbus serial-clock input 15 15 stby input. hardware standby. connect to ground to place in device in standby. supply current drops below 10? and all registers?data are maintained. input. selects which temperature sensor (local, remote, or both) activates overt . 16 16 sens_sel high = remote, low = local, open = local and remote
max6680/max6681 detailed description the max6680/max6681 are temperature sensors designed to work in conjunction with a microprocessor or other intelligence in thermostatic, process-control, or monitoring applications. communication with the max6680/max6681 occurs through the smbus serial interface and dedicated alert pin. the overtemperature alarm overt is asserted if the software or hardware programmed temperature thresh- olds are exceeded. overt can be connected to a fan, system shutdown, or other thermal management circuitry. the max6680/max6681 convert temperatures at a pro- grammed rate or a single conversion. legacy mode conversions have a 1? resolution. legacy resolution represents temperature as 7 bits + sign bit and allows for faster autonomous conversion rates at 8hz. the remote diode temperature can also be represented in extended-resolution mode. extended resolution repre- sents temperature as 10 bits + sign bit and is available for autonomous conversions that are 4hz or slower and single-shot conversions. the max6680/max66681 default low-temperature mea- surement limit is 0 ?. the device temperature measure- ment can be placed in extended temperature range by setting bit 3 of the configuration register to 1. in extend- ed temperature range, the remote and local temperature measurement range is extended down to -64?. adc and multiplexer the averaging adc integrates over a 60ms period (each channel, typically, in the 7-bit + sign ?egacy mode). using an averaging adc attains excellent noise rejection. the multiplexer automatically steers bias currents through the remote and local diodes. the adc and associated circuitry measure each diode? forward volt- ?? fail-safe remote/local temperature sensors with smbus interface 6 _______________________________________________________________________________________ reset circuitry mux remote local adc 2 control logic smbus read write 8 8 address decoder 7 s r q diode fault dxp dxn add0 smbclk smbdata add1 register bank command byte remote temperature local temperature alert threshold alert response address overt threshold (ext) overt threshold (int) crit0 crit1 int_sel stby reset v cc s r q overt alert sens_sel max6680 max6681 figure 1. max6680/max6681 functional diagram
age and computes the temperature based on this volt- age. if the remote channel is not used, connect dxp to dxn. do not leave dxp and dxn unconnected. when a conversion is initiated, both channels are con- verted whether or not they are used. the dxn input is biased at one v be above ground by an internal diode to set up the adc inputs for a differential measurement. resistance in series with the remote diode causes about 1/2? error per ohm. a/d conversion sequence a conversion sequence consists of a local temperature measurement and a remote temperature measurement. each time a conversion begins, whether initiated auto- matically in the free-running autoconvert mode (run/stop = 0) or by writing a one-shot command, both channels are converted, and the results of both measurements are available after the end of conver- sion. a busy status bit in the status register shows that the device is actually performing a new conversion. the results of the previous conversion sequence are still available when the adc is busy. remote-diode selection the max6680/max6681 can directly measure the die temperature of cpus and other ics that have on-board temperature-sensing diodes (see the typical operating circuit ) or they can measure the temperature of a dis- crete diode-connected transistor. the type of remote diode used is set by bit 5 of the configuration byte. if bit 5 is set to zero, the remote sensor is a diode-con- nected transistor, and if bit 5 is set to 1, the remote sen- sor is a substrate or common-collector pnp transistor. for best accuracy, the discrete transistor should be a small-signal device with its collector and base connect- ed together. accuracy has been experimentally verified for all of the devices listed in table 1. the transistor must be a small-signal type with a rela- tively high forward voltage; otherwise, the a/d input voltage range can be violated. the forward voltage at the highest expected temperature must be greater than 0.25v at 10?, and at the lowest expected tempera- ture, forward voltage must be less than 0.95v at 100?. large power transistors must not be used. also, ensure that the base resistance is less than 100 ? . tight speci- fications for forward-current gain (50 < ?< 150, for example) indicate that the manufacturer has good process controls and that the devices have consistent v be characteristics. thermal mass and self-heating when sensing local temperature, these temperature sensors are intended to measure the temperature of the pc board to which they are soldered. the leads pro- vide a good thermal path between the pc board traces and the die. thermal conductivity between the die and the ambient air is poor by comparison, making air-tem- perature measurements impractical. because the ther- mal mass of the pc board is far greater than that of the max6680/max6681, the device follows temperature changes on the pc board with little or no perceivable delay. when measuring the temperature of a cpu or other ic with an on-chip sense junction, thermal mass has virtu- ally no effect; the measured temperature of the junction tracks the actual temperature within a conversion cycle. when measuring temperature with discrete remote sen- sors, smaller packages (e.g., a sot23) yield the best thermal response times. take care to account for ther- mal gradients between the heat source and the sensor, and ensure that stray air currents across the sensor package do not interfere with measurement accuracy. self-heating does not significantly affect measurement accuracy. remote-sensor self-heating due to the diode current source is negligible. for the local diode, the worst-case error occurs when autoconverting at the fastest rate and simultaneously sinking maximum cur- rent at the alert output. for example, with v cc = 5.0v, an 8hz conversion rate, and alert sinking 1ma, the typical power dissipation is v cc ? 550? + 0.4v ? 1ma, which equals 2.75mw; j-a for the 16-pin qsop package is about +120?/w, so assuming no copper pc board heat sinking, the resulting temperature rise is: even under these engineered circumstances, it is diffi- cult to introduce significant self-heating errors. adc noise filtering the integrating adc used has good noise rejection for low-frequency signals such as 60hz/120hz power-sup- ? tmw cw c == 2 75 120 0 330 ./. max6680/max6681 ?? fail-safe remote/local temperature sensors with smbus interface _______________________________________________________________________________________ 7 manufacturer model no. central semiconductor (usa) cmpt3904 on semiconductor (usa) 2n3904, 2n3906 rohm semiconductor (usa) sst3904 samsung (korea) kst3904-tf siemens (germany) smbt3904 zetex (england) fmmt3904ct-nd table 1. remote-sensor transistor manufacturers note: transistors must be diode connected (base shorted to collector).
max6680/max6681 ply hum. in noisy environments, high-frequency noise reduction is needed for high-accuracy remote mea- surements. the noise can be reduced with careful pc board layout and proper external noise filtering. high-frequency emi is best filtered at dxp and dxn with an external 2200pf capacitor. larger capacitor values can be used for added filtering, but do not exceed 3300pf because it can introduce errors due to the rise time of the switched current source. pc board layout follow these guidelines to reduce the measurement error of the temperature sensors: 1) place the max6680/max6681 as close as is practi- cal to the remote diode. in noisy environments, such as a computer motherboard, this distance can be 4in to 8in (typ). this length can be increased if the worst noise sources are avoided. noise sources include crts, clock generators, memory buses, and isa/pci buses. 2) do not route the dxp-dxn lines next to the deflec- tion coils of a crt. also, do not route the traces across fast digital signals, which can easily intro- duce 30? error, even with good filtering. 3) route the dxp and dxn traces in parallel and in close proximity to each other, away from any higher voltage traces, such as 12vdc. leakage currents from pc board contamination must be dealt with care- fully since a 20m ? leakage path from dxp to ground causes about 1? error. if high-voltage traces are unavoidable, connect guard traces to gnd on either side of the dxp-dxn traces (figure 2). 4) route through as few vias and crossunders as pos- sible to minimize copper/solder thermocouple effects. 5) when introducing a thermocouple, make sure that both the dxp and the dxn paths have matching thermocouples. a copper-solder thermocouple exhibits 3?/?, and it takes about 200? of voltage error at dxp-dxn to cause a 1? measurement error. adding a few thermocouples causes a negligi- ble error. 6) use wide traces. narrow traces are more inductive and tend to pick up radiated noise. the 10mil widths and spacings that are recommended in figure 2 are not absolutely necessary, as they offer only a minor improvement in leakage and noise over narrow traces. use wider traces when practical. 7) add a 200 ? resistor in series with v cc for best noise filtering (see the typical operating circuit ). twisted-pair and shielded cables use a twisted-pair cable to connect the remote sensor for remote-sensor distances longer than 8in or in very noisy environments. twisted-pair cable lengths can be between 6ft and 12ft before noise introduces excessive errors. for longer distances, the best solution is a shielded twisted pair like that used for audio micro- phones. for example, belden 8451 works well for dis- tances up to 100ft in a noisy environment. at the device, connect the twisted pair to dxp and dxn and the shield to gnd. leave the shield unconnected at the remote sensor. for very long cable runs, the cable? parasitic capaci- tance often provides noise filtering, so the 2200pf capacitor can often be removed or reduced in value. cable resistance also affects remote-sensor accuracy. for every 1 ? of series resistance, the error is approxi- mately 1/2? error. low-power standby mode standby mode reduces the supply current to less than 10? by disabling the adc. enter hardware standby by forcing the stby pin low, or enter software standby by setting the run/stop bit to 1 in the configuration byte register. hardware and software standbys are very sim- ilar: all data is retained in memory, and the smb inter- face is alive and listening for smbus commands, but the smbus timeout is disabled. the only difference is that in software standby mode, the one-shot command initiates a conversion. with hardware standby, the one- shot command is ignored. activity on the smbus caus- es the device to draw extra supply current (see the typical operating characteristics ). driving the stby pin low overrides any software con- version command. if a hardware or software standby command is received while a conversion is in progress, the conversion cycle is interrupted, and the tempera- ?? fail-safe remote/local temperature sensors with smbus interface 8 _______________________________________________________________________________________ minimum 10mils 10mils 10mils 10mils gnd dxn dxp gnd figure 2. recommended dxp-dxn pc traces
ture registers are not updated. the previous data is not changed and remains available. smbus digital interface from a software perspective, the max6680/max6681 appear as a series of 8-bit registers that contain tem- perature data, alarm threshold values, and control bits. a standard smbus-compatible 2-wire serial interface is used to read temperature data and write control bits and alarm threshold data. the device responds to the same smbus slave address for access to all functions. the max6680/max6681 employ four standard smbus protocols: write byte, read byte, send byte, and receive byte (figure 3). the shorter receive byte pro- tocol allows quicker transfers, provided that the correct data register was previously selected by a read byte instruction. use caution with the shorter protocols in multimaster systems, since a second master could overwrite the command byte without informing the first master. when the conversion rate is 8hz, temperature data can be read from the read internal temperature (00h) and read external temperature (01h) registers. the tem- perature data format in these registers is 7 bits + sign in two?-complement form for each channel, with the lsb representing 1? (table 2). the msb is transmitted first. extended range extends the temperature data range of the local and remote sensor to -64?. extended range is activated by setting bit 3 of the configuration register to 1. when the conversion rate is 4hz or less, temperature data can be read from the read internal temperature (00h) and read external temperature (01h) registers, the same as for faster conversion rates. an additional 3 bits can be read from the read external extended temperature (10h), which extends the remote tempera- ture data to 10 bits + sign and the resolution to 0.125? per lsb (table 3). when a conversion is complete, the main register and the extended register are updated almost simultane- ously. ensure that no conversions are completed between reading the main and extended registers so that when data that is read by both registers contain the result of the same conversion. max6680/max6681 ?? fail-safe remote/local temperature sensors with smbus interface _______________________________________________________________________________________ 9 ack 7 bits address ack wr 8 bits data ack 1 p 8 bits s command write byte format read byte format send byte format receive byte format slave address: equiva- lent to chip-select line of a 3-wire interface command byte: selects which register you are writing to data byte: data goes into the register set by the command byte (to set thresholds, configuration masks, and sampling rate) ack 7 bits address ack wr s ack 8 bits data 7 bits address rd 8 bits /// p command slave address: equiva- lent to chip-select line command byte: selects which register you are reading from slave address: repeated due to change in data- flow direction data byte: reads from the register set by the command byte ack 7 bits address wr 8 bits command ack p ack 7 bits address rd 8 bits data /// p s command byte: sends com- mand with no data, usually used for one-shot command data byte: reads data from the register commanded by the last read byte or write byte transmission; also used for smbus alert response return address s = start condition shaded = slave transmission p = stop condition /// = not acknowledged figure 3. smbus protocols
max6680/max6681 to ensure valid extended data, read extended resolu- tion temperature data using one of the following approaches: 1) put the max6680/max6681 into standby mode by setting bit 6 of the configuration register to 1. initiate a one-shot conversion using send byte command 0fh. when this conversion is complete, read the contents of the temperature data registers. 2) if the max6680/max6681 are in run mode, read the status register. if a conversion is in progress, the busy bit is set to 1. wait for the conversion to com- plete as indicated by the busy bit being set to zero, then read the temperature data registers. diode fault alarm there is a continuity fault detector at dxp that detects an open circuit between dxp and dxn, or a dxp short to v cc , gnd, or dxn. if an open or short circuit exists, the external temperature register is loaded with 1000 0000. additionally, if the fault is an open circuit, bit 2 (open) of the status byte is set to 1 and the alert condition is activated at the end of the conversion. immediately after power-on reset, the status register indicates that no fault is present until the end of the first conversion. alarm threshold registers four registers store alert threshold values?ne high- temperature (t high ) and one low-temperature (t low ) register each for the local and remote channels. if either measured temperature equals or exceeds the corresponding alert threshold value, the alert out- put is asserted. the por state of both alert t high registers is 0111 1111 or +127? and the por state of t low registers is 1100 1001 or -55?. two additional registers, rwoe and rwoi, store remote and local alarm threshold data information cor- responding to the overt output (see the overt overtemperature alarm section). alert the alert output operates in two modes?he typical interrupt mode and comparator mode. the int_sel input determines the mode. when int_sel is connect- ed to v cc high, using a weak pullup resistor, or left floating, the alert functions in the interrupt mode. alert interrupt mode an alert interrupt occurs when the internal or external temperature reading exceeds a high or low tempera- ture limit (user programmed) or when the remote diode is disconnected (for continuity fault detection). the alert interrupt output signal is latched and can be cleared only by either reading the status register or by successfully responding to an alert response address. in both cases, the alert is cleared even if the fault con- dition still exists, but is reasserted at the end of the next conversion. the interrupt does not halt automatic con- versions. the interrupt output pin is open drain so that multiple devices can share a common interrupt line. the interrupt rate never exceeds the conversion rate. comparator mode connecting int_sel to ground operates the alert output in comparator mode. in the comparator mode, whenever the temperature of the remote or local temp sensor goes outside the limits set by t high or t low , the alert output becomes inactive after the tempera- ?? fail-safe remote/local temperature sensors with smbus interface 10 ______________________________________________________________________________________ temp ( c) legacy mode digital output extended range digital output 127.00 0111 1111 0111 1111 25 0001 1001 0001 1001 1 0000 0001 0000 0001 0.00 0000 0000 0000 0000 -1 0000 0000 1111 1111 -25 0000 0000 1110 0111 -64 0000 0000 1000 0000 diode fault (short or open) 1000 0000 1000 0000 table 2. data format (two? complement) fractional temperature contents of extended register 0.000 000x xxxx 0.125 001x xxxx 0.250 010x xxxx 0.375 011x xxxx 0.500 100x xxxx 0.625 101x xxxx 0.750 110x xxxx 0.875 111x xxxx table 3. extended resolution register note: extended mode applies only for conversion rates of 4hz and slower.
ture returns within the limits. an open diode also sets this output. alert response address the smbus alert response interrupt pointer provides quick fault identification for simple slave devices that lack the complex, expensive logic needed to be a bus master. upon receiving an alert interrupt signal, the host master can broadcast a receive byte transmission to the alert response slave address (see the slave addresses section). then, any slave device that gener- ated an interrupt, attempts to identify itself by putting its own address on the bus (table 4). the alert response can activate several different slave devices simultaneously, similar to the i 2 c general call. if more than one slave attempts to respond, bus arbitra- tion rules apply, and the device with the lower address code wins. the losing device does not generate an acknowledge and continues to hold the alert line low until cleared. (the conditions for clearing an alert vary max6680/max6681 ?? fail-safe remote/local temperature sensors with smbus interface ______________________________________________________________________________________ 11 smbclk ab cd e fg h i j k smbdata t su:sta t hd:sta t low t high t su:dat t hd:dat t su:sto t buf a = start condition b = msb of address clocked into slave c = lsb of address clocked into slave d = r/w bit clocked into slave e = slave pulls smbdata line low l m f = acknowledge bit clocked into master g = msb of data clocked into slave h = lsb of data clocked into slave i = master pulls data line low j = acknowledge clocked into slave k = acknowledge clock pulse l = stop condition m = new start condition figure 4. smbus write timing diagram smbclk ab cd e fg h i j k smbdata t su:sta t hd:sta t low t high t su:dat t hd:dat t su:sto t buf l m a = start condition b = msb of address clocked into slave c = lsb of address clocked into slave d = r/w bit clocked into slave e = slave pulls smbdata line low f = acknowledge bit clocked into master g = msb of data clocked into master h = lsb of data clocked into master i = master pulls data line low j = acknowledge clocked into slave k = acknowledge clock pulse l = stop condition m = new start condition figure 5. smbus read timing diagram
max6680/max6681 depending on the type of slave device.) successful completion of the alert response protocol clears the interrupt latch, provided the condition that caused the alert no longer exists. if the condition still exists, the device reasserts the alert interrupt at the end of the next conversion. overt overtemperature alarm two registers, rwoe and rwoi, store remote and local alarm threshold data corresponding to the overt out- put. the values stored in these registers are high-tem- perature thresholds. if any one of the measured temperatures equals or exceeds the corresponding alarm threshold value, an overt output is asserted. the overtemperature thresholds are both hardware and software programmable. the overtemperature thresh- olds can be hardware programmed by pin strapping crit0 and crit1. use table 4 to set the desired remote and local threshold temperatures. upon por or driving the reset pin high, the overtemperature regis- ter takes on the hardware-programmed values. afterward, any write to the overtemperature registers overwrites the hardware-programmable values. overt always operates in comparator mode and is asserted when the temperature rises to a value pro- grammed in the appropriate threshold register. it is deasserted when the temperature drops below this threshold minus the programmed value in the hysteresis (hyst) register. an overt output can be used to acti- vate a cooling fan, send a warning, initiate clock throt- tling, or trigger a system shutdown to prevent component damage. the hyst byte sets the amount of hysteresis to deassert the overt output. the data format for the hyst byte is 7 bits + sign with 1? resolution. bit 7 of the hyst register should always be zero. command byte functions the 8-bit command byte register (table 5) is the mas- ter index that points to the various other registers within the max6680/max6681. this register? por state is 0000 0000, so a receive byte transmission (a protocol that lacks the command byte) occurring immediately after por returns the current local temperature data. one shot the one-shot command immediately forces a new con- version cycle to begin. if the one-shot command is received when the max6680/max6681 is in software standby mode (run/stop bit = 1), a new conversion is begun, after which the device returns to standby mode. if a conversion is in progress when a one-shot com- mand is received, the command is ignored. if a one-shot command is received in autoconvert mode ( run/stop bit = 0) between conversions, a new conversion begins, the conversion rate timer is reset, and the next automatic conversion takes place after a full delay elapses. configuration byte functions the configuration byte register, table 6, is a read-write register with several functions. bit 7 is used to mask (disable) alert interrupts. bit 6 puts the device into software standby mode (stop) or autonomous (run) mode. bit 5 selects the type of external junction (set to 0 for a substrate pnp on an ic or set to 1 for a discrete diode-connected transistor) for optimized measure- ments. bit 4 selects the extended temperature mea- surement for the remote sensor. if high, the temperature data is available as 10 bits + sign with a 0.125? reso- lution, otherwise, 7 bits + sign with 1? resolution. bit 4 extends the temperature range of the remote and local temperature sensor to -64?. bit 2 disables the smbus timeout, as well as the alert response. bit 1 provides a software reset from the smbus. bit 0 is reserved and returns a zero when read. status byte functions the status byte (table 7) indicates which (if any) tem- perature thresholds have been exceeded. this byte also indicates whether the adc is converting and if there is an open-circuit fault detected with the external sense junction. after por, the normal state of the regis- ters?bits is zero, assuming no alert or overtemperature conditions are present. when operating the max6680/max6681 in alert interrupt mode, bits 2 through 6 of the status register are cleared by any suc- cessful read of the status register, unless the fault per- sists. the alert output follows the status flag bit. both are cleared when successfully read, but if the condition ?? fail-safe remote/local temperature sensors with smbus interface 12 ______________________________________________________________________________________ overt threshold (?) crit1 crit0 remote local gnd gnd +85 +70 gnd open +90 +75 gnd v cc +95 +80 open gnd +100 +85 open open +105 +90 open v cc +110 +95 v cc gnd +115 +100 v cc open +120 +105 v cc v cc +125 +110 table 4. overt temperature threshold programming
still exists, they are reasserted at the end of the next conversion. if the max6680/max6681 are operating in the comparator mode, bits 2? of the status register are cleared only after the local and/or remote tempera- tures return within the set limits. the bits indicating ovti and ovte are cleared only when the condition no longer exists. reading the status byte does not clear the overt output or fault bits. one way to eliminate the fault condition is for the measured temperature to drop below the temperature threshold minus the hysteresis value. another way to eliminate the fault condition is by writing new values for the rwoi, rwoe, or hyst registers so that a fault condi- tion is no longer present. the max6680/max6681 incorporate collision avoid- ance so that completely asynchronous operation is allowed between smbus operations and temperature conversions. when autoconverting, if the t high and t low limits are close together, it is possible for both high-temp and low-temp status bits to be set, depending on the amount of time between status read operations. in these circumstances, it is best not to rely on the status bits to indicate reversals in long-term temperature changes. instead use a current temperature reading to establish the trend direction. hardware/software reset the max6680/max6681 reset at power-on if pin 7 is taken high, or by software reset through bit 1 of the configuration register. when reset occurs, all registers go to default values, and the smbus address pins are sampled. conversion rate byte the conversion rate register (table 8) programs the time interval between conversions in free-running max6680/max6681 ?? fail-safe remote/local temperature sensors with smbus interface ______________________________________________________________________________________ 13 register address por state function rlts 00h 0000 at 0? read internal temperature rrte 01h 0000 (0?) read external temperature rsl 02h 0000 0000 read status register rcl/wcl 03h/09h 0010 0000 read/write configuration byte rcra/wcra 04h/0a 0000 0010 read/write conversion rate byte rih/wih 05h/0bh 0111 1111 (+127?) read/write internal alert high limit ril/wil 06h/0ch 1100 1001 ( -55?) read/write internal alert low limit reh/weh 07h/0dh 0100 0110 (+127?) read/write external alert high limit rel/wel 08h/0eh 1100 1001 (-55?) read/write external alert low limit osht 0fh 0000 one shot reet 10h 0000 0000 read external extended temperature rwoh 11h 0000 0000 read/write external offset high byte rwol 12h 0000 0000 read/write external offset low byte rwoe 19h see table 4 read/write external overt limit rwoi 20h see table 4 read/write internal overt limit hyst 21h 0000 0110 (+6?) overt hysteresis rdid feh 0100 1101 read manufacturer id rdrv ff 0000 0001 read device revision table 5. command-byte register bit assignments
max6680/max6681 autonomous mode (run/stop = 0). this variable rate control can be used to reduce the supply current in portable-equipment applications. the conversion rate byte? por state is 02h (0.25hz). the max6680/ max6681 use only the 3lsbs of this register. the 5msbs are ?on? care?and should be set to zero when possible. the conversion rate tolerance is ?5% at any rate setting. valid a/d conversion results for both channels are avail- able one total conversion time (125ms nominal, 156ms maximum) after initiating a conversion, whether conver- sion is initiated through the run/stop bit, hardware stby pin, one-shot command, or initial power-up. slave addresses the max6680/max6681 device address can be initially set to nine different values by pin strapping add0 and add1 so that more than one max6680/max6681 can ?? fail-safe remote/local temperature sensors with smbus interface 14 ______________________________________________________________________________________ bit name por state function 7 (msb) alert mask 0 mask alert active state when 1. when 1, alert does not respond to any fault related to the four limit registers. 6 run/stop 0 standby mode control bit; if 1, immediately stops converting and enters standby mode. if zero, it converts in either one-shot or timer mode. 5 spnp 1 when 1, the remote sensor is a common-collector substrate pnp. when zero, the remote sensor is a diode-connected transistor. 4 extended resolution 0 when zero, remote- and local-sensors?temperature data are 7 bits + sign with 1? resolution. when 1, the remote-sensor temperature data is 10 bits + sign with 0.125? resolution. 3 extended range 0 extended temperature range. 0 = normal, 1 = extended to -64?. 2 smbus timeout 0 when set to 1, it disables the smbus timeout, as well as the alert response. 1 software reset 0 software reset from smbus from customer. 0 rfu 0 reserved table 6. configuration-byte bit assignment bit name por state function 7 (msb) busy 0 when 1, the a/d is busy converting. 6 lhigh 0 when 1, internal high-temperature alarm has tripped; cleared by por or readout of the status register, if the fault condition no longer exists. 5 llow 0 when 1, internal low-temperature alarm has tripped; cleared by por or readout of the status register, if the fault condition no longer exists. 4 rhigh 0 when 1, external high-temperature alarm has tripped; cleared by por or readout of the status register, if the fault condition no longer exists. 3 rlow 0 when 1, external low-temperature alarm has tripped; cleared by por or readout of the status register if the fault condition no longer exists. 2 open 0 when 1 indicates an external diode open; cleared by por or readout of the status register, if the fault condition no longer exists. 1 ovi 0 when 1, internal temperature exceeds the rwoi limit. 0 ove 0 when 1, external temperature exceeds the rwoe limit. table 7. status register bit assignments
reside on the same bus without address conflicts (table 9). the address pin states are checked at por and reset only, and the address data stays latched to reduce qui- escent supply current due to the bias current needed for high-z state detection. the max6680/max6681 also respond to the smbus alert response slave address (see the alert response address section). por and uvlo the max6680/max6681 have a volatile memory. to prevent unreliable power-supply conditions from cor- rupting the data in memory and causing erratic behav- ior, a por voltage detector monitors v cc and clears the memory if v cc falls below 1.91v (typ, see electrical characteristics ). when power is first applied and v cc rises above 2.0v (typ), the logic blocks begin operating, although reads and writes at v cc levels below 3.0v are not recommended. a second v cc comparator, the adc uvlo comparator, prevents the adc from converting until there is sufficient headroom (v cc = 2.8v typ). power-up defaults interrupt latch is cleared. address select pin is sampled. adc begins autoconverting at a 1hz rate (legacy resolution). command register is set to 00h to facilitate quick internal receive byte queries. ? high and t low registers are set to max and min limits, respectively. hysteresis is set to 6?. transistor type is set to a substrate or common-col- lector pnp. temperature offset the max6680/max6681 are designed to provide ?? accuracy for common microprocessors and discrete transistors. to accommodate processes that differ sig- nificantly in their ideality factor, the user can increase/decrease the remote temperature sensor data register with an offset by writing to the external offset high and low byte registers (11h and 12h, respectively). the offset temperature data is represent- ed as a 10 bits + sign with a 0.125lsb resolution. max6680/max6681 ?? fail-safe remote/local temperature sensors with smbus interface ______________________________________________________________________________________ 15 data conversion rate (hz) 00h 0.0625 01h 0.125 02h 0.25 03h 0.5 04h 1 05h 2 06h 4 07h 8 table 8. conversion-rate control byte note: if extended resolution is selected using bit 4 of the configuration register, the extended conversion is limited to a maximum of 4hz. add0 add1 address gnd gnd 0011 000 gnd high-z 0011 001 gnd v cc 0011 010 high-z gnd 0101 001 high-z high-z 0101 010 high-z v cc 0101 011 v cc gnd 1001 100 v cc high-z 1001 101 v cc v cc 1001 110 table 9. por slave address decoding (add0 and add1) chip information transistor count: 17,150 process: bicmos
max6680/max6681 ?? fail-safe remote/local temperature sensors with smbus interface 16 ______________________________________________________________________________________ 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 v cc sens_sel stby smbclk int_sel smbdata alert addo overt top view max6680 qsop crit1 dxp add1 dxn crit0 reset gnd 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 v cc sens_sel stby smbclk int_sel smbdata alert addo overt max6681 qsop crit1 dxp add1 dxn crit0 reset gnd pin configurations
max6680/max6681 ?? fail-safe remote/local temperature sensors with smbus interface maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ____________________ 17 2005 maxim integrated products printed usa is a registered trademark of maxim integrated products, inc. qsop.eps e 1 1 21-0055 package outline, qsop .150", .025" lead pitch package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation, go to www.maxim-ic.com/packages .)

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